Induction coil



March 25, 1941. A. HELGASON INDUCTION COIL Filed Aug. 18, 1939 fiaamPatented Mar. 25, 1941 PATENT OFFICE INDUCTION COIL Arni Helgason,Chicago, Ill., assignor to Chicago Transformer Corporation, acorporation of Illinois Application August 18, 1939, Serial No. 290,814

Claims.

This invention relates to induction coils and particularly to coils forhigh speed internal combustion engines. Due to the number of cylindersand speed of modern engines, the time for 5 generating an ignitioncurrent is extremely small. Hence coils having low inductance must beused. To improve the efficiency of such coils it hasbeen the custom totaper the'secondary width to a minimum outer larger width and at thesame time use long laminations whose ends are bent around the coil afterinsertion therein. Such a construction is shown in Patent 1,908,798 toToelle.

The construction of the coil shown in this patent involves difiicultiesfor testing. The complete coil must pass a rigid test for inductance andmust perform satisfactorily, the tolerances being rather narrow.

Coils of this type are cased in a moulded housing with rather a snugfit. This case serves to press the core ends down tightly into positionand the working conditions of the coil presuppose such a core condition.Hence to test a coil properly, such conditions should be duplicated.

It is desirable to test the coils prior to encasing since removal of acoil from its housing for adjustment purposes is too difficult and timeconsuming.

In the Toelle structure, the bending of the laminations around the coilmakes the testing of such a coil difiicult. Due to the spring of themetal and the lack of precision of the shaping of the steel strips, somesubstitute for the final housing must be used in the test if theinductance of the coil under operating conditions is to be duplicated.

In accordance with this invention, I have modifled the construction ofthe Toelle patent so that the above dificulties are eliminated. Ingeneral,

my invention contemplates pre-shaping the laminations in such a mannerthat variations in the reluctance of the magnetic circuit are reduced tonegligible proportions. This pre-shaping or preforming contemplates theactual bending of the steel, and is to be distinguished from stampinglaminations.

Stamping of laminations for ignition coils, that is, using fiat stampedlaminations, has been attempted with some success but involves somerather serious difliculties. Thus, because of the coil shape, it isimpossible to stamp out one lamination whose ends would curl around thecoil as shown in the Toelle patent. If the strip is divided at the coilinterior, then variations in air gap become serious. In a coil of thischaracter, an air gap variation in the coil interior is much morecritical than on the exterior of the .coil. A short straight gap acrossthe ship within the coil is therefore out of consider- I ation.Increasing the gap length by shaping the 5 end of the strip greatlyincreases steel waste in stamping.

By my invention, I am enabled to produce an ignition coil such as shownby Toelle in his patent in quantity production without in any way 10compromising the excellence or characteristics thereof and yet withoutexcessive production costs.

Referring to the drawing:

Fig. 1 shows a sectional view of a coil embodying the present invention;

Fig. 2 is a detail of one of the members for clamping the laminations inposition;

Fig. 3 is a detail of the other member cooperating with the member shownin Fig. 2; 20

Fig. 4 shows an outline view of a coil having a shaping member on theoutside of the laminations; and

Fig. 5 shows a lamination.

The coil comprises a tube ill suitably shaped of stiff insulatingmaterial upon which is wound a primary winding ii of coarse wire. Thiswinding may be composed of several layers of wire preferably extendingthe full length of the coil. Disposed over primary winding ii andsuitably 3Q insulated therefrom is a secondary winding Q2 of fine wire.This secondary tapers from the bottom layer which is somewhat shorterthan the primary coil up to the top or outer layer. It is understood, ofcourse, that suitable insulation is 85 provided. The entire coil maythen be wrapped with suitable insulating material iii.

Within insulating tube iii are disposed four groups of laminationsnumbered it to i9 inclusive. The various groups of laminations are all(it similar so that only one need be described in detail. Thus,referring to group it, this group is composed of a number of laminationshaving a long straight portion 20 and a curved portion 2| adapted tooverlie the end of the coil and ter- 45 minating in a tip 2'2. Each ofthese laminations is made of suitable steel and shaped so that the groupnest as shown. The shaping of the laminations may be accomplished in anysuitable manner such as by bending a single lamination or group oflaminations over a suitable metal plate.

In the bending of the lamination groups, it is preferred to make a sharpright angle 23 in the innermost lamination 24 of eachgroup and shape theremaining strips accordingly. In this way, Iii

the free end of straight portion 20 of each group can extend right up tothe abutting lamination. In this connection it should be observed thatthe straight portions 20 of the laminations should 5 be alined at theirfree ends so that any possible air gap variation be reduced to aminimum.

As clearly shown in Fig, 1 the laminations for each group are disposedadjacent to each other to form a compact unit. Group I! of the lamiinations has its long portion 20 disposed adjacent the correspondingportion of group 86. Groups i9 and 18 are disposed in correspondingrelation to each other in a manner similar to groups it and El.

15 In order to maintain the entire transformer intact, suitable clampmeans is provided. Thus as shown in Figs. 2 and 3, a sheet metal memberof a general T-shape is provided. This metal member has a body 25 havingits end 28 split at 20 ill. The head is provided with a cross-member 28whose sides 29 are bent over to form flanges. The head 28 is in theshape shown so that the entire member may be stamped out of a singlepiece of metal. The width of head 28 is equal to 25 the width of eachlamination and the sides 29 are adapted to lie along the edges of eachgroup of laminations.

Member 25 is disposed preferably along the center of the space occupiedby the straight por- 3 tions 29 of the laminations and extends the fulllength of the coil. Cooperating with portion 25 is a small u shapedmember 33 whose sides 3i are flanged in a manner similar to that of head28. Member 3b is provided with a slot 32 transversely thereof into whichend 28 of member 25 is adapted to fit. The end 26 passes through theslot and the two portions opposite slit 2? are then bent on oppositesides to lock the entire assembly.

If desired, heavy retaining members 35' and 36 suitably shaped may bedisposed over each end or the coil to fit over the end group oflaminations. In this way, an iron clad construction is provided.

What is claimed is:

1. An induction coil comprising a straight primary winding, a secondarywinding superposed and concentric with said primary winding, saidsecondary winding consisting of a plurality of layers of wire with thelayer adjacent the primary having the greatest number of turns and withthe succeeding layers having less turns, and a magnetizing core, saidmagnetizing core-comprising preformed and preshaped laminations dividedinto four groups, each group of laminations consisting of nestedindividual laminations having one end portion straight and disposedwithin the interior of said windings and extending the full coil lengthand the other end portion bent along lines parallel to the width of thestrip and following the coil around the end and outer surface toward themiddle part of the coil, two groups extending from one coil endbut bentaway from each other along the coil end, the remaining two groupsextending from the other coll end and bent away from each other, onegroup of the first-mentioned two groups and one group of the secondmentioned two groups having the portions on the outer coil surfaceextending toward each other and forming an air gap at the middle part ofthe coil, the remaining groups forming a similar air gap on the outercoil surface on the other side of the coil and means for maintainingsaid laminations on said coil .whereby there results an ignition coilhaving a small time constant and high eficiency and whose inductance maybe closely controlled in production.

2. The induction coil of claim 1 wherein said means for maintaining saidlaminations consists of a clamping means engaging said laminations atopposite ends of said coil.

3. The structure of claim 1 wherein said means for maintaining saidlaminations consists of a heavy strip of metal extending along theoutside of two groups of laminations at one end of the coil and asimilar strip along the outside of the other two groups and means formaintaining said strips rigidly in position.

a. An induction coil comprising an elongated primary winding, asecondary winding disposed in concentric relation to the primary withsaid secondary winding consisting of a plurality of layers of wiretapering symmetrically with respect to said primary from a bottom layerhaving 39 the greatest number of turns to a top layer having thesmallest number of turns, and a laminated preformed preshapedmagnetizing core for said coil, said core consisting of four groups oflaminations, each group consisting of a plurality of fiat preshapednested laminations with an end portion of each lamination being straightand disposed within the interior of said coil and extending the fullcoil length and the other end portion being curved along lines parallelto the 40 Width thereof and following the coil around the end and outersurface toward the middle part of the coil, two groups extending fromone coil end but bent away from each other along the coil end, theremaining two groups extending from the 35 other coil and and bent awayfrom each other, one group of the first-mentioned two groups and onegroup of the second mentioned two groups having the portions on theouter coil surface extending toward each other and forming an air gapvatthe middle part of the coil, the remaining groups forming a similar airgap on the outer coil surface on the other side or the coil and meansfor maintaining said groups rigidly in position whereby there results anignition coil having a small time constant and high emciency and whoseinductance may be closely controlled in production.

5. The structure of claim 4 wherein said lastnamed means consists of anI-shaped structure gr with the end pieces extending along the ]ainina-=tions at the coil ends and the connecting strip extending between thelamination groups along the coil interior.

ARNI HELGASON. g:

